Hi D.B Ko!
Thanks for sharing with us photos of your Thor! It looks impressive! 🙂
Regarding your questions:
– Art3&Art4 Union: There are a piece called Art4BearingRing and other one called Art4TransmissionColumn. You will need to insert 30 small balls (Diameter 6mm) between this pieces trough the small hole placed in one side of the Art4BearingRing piece. I have used 6mm airsoft balls and it works very well. I know that is not the same version (is the one that is not already tested) but I did an animation of the assembly that you can check here. As almost all pieces are very similar I think it would help you in the assembly.
– PCB Power supply: 12V/3A will not be enough to bring power to the 7 steppers of the robot. I’m currently using a power supply of 12V/7A and it seems to be enough.
Hope it helps!